1. Field of the Invention
The present invention relates to electronic driving devices, and particularly to a device for driving a light source module, typically used for changing polarities of output voltages thereof.
2. Related Art
Generally, discharge lamps have been used as light sources of a liquid crystal display (LCD) panel, which need high voltage to light up the light sources. With large size LCD panels, a plurality of lamps is required for providing sufficient light intensity in the LCD panel.
FIG. 6 shows a schematic diagram of a conventional driving device connected to a light source module having a plurality of lamps L1n (n=1, 2, 3, . . . , n). The conventional driving device includes a power stage circuit 10 and a plurality of transformers T1n (n=1, 2, 3, . . . , n). Each of the transformers T1n (n=1, 2, 3, . . . , n) includes a primary winding and a secondary winding. Each of the primary windings has a first input a1n (n=1, 2, 3, . . . , n) and a second input b1n (n=1, 2, 3, . . . , n), and each of secondary windings has a high voltage terminal c1n (n=1, 2, 3, . . . , n) and a low voltage terminal d1n (n=1, 2, 3, . . . , n). The first inputs a1n (n=1, 2, 3, . . . , n) of the primary windings of the transformers T1n (n=1, 2, 3, . . . , n) are jointly connected to one output of the power stage 10. Similarly, the second inputs b1n (n=1, 2, 3, . . . , n) of the primary windings of the transformers T1n (n=1, 2, 3, . . . , n) are jointly connected to another output of the power stage 10. The high voltage terminals c1n (n=1, 2, 3, . . . , n) of the secondary winding of the transformers T1n (n=1, 2, 3, . . . , n) are respectively connected to the lamps L1n (n=1, 2, 3, . . . , n), and the low voltage terminals d1n (n=1, 2, 3, . . . , n) of the secondary winding of the transformers T1n (n=1, 2, 3, . . . , n) are grounded.
In the conventional driving device, because structures and the characteristics of the transformers T1n (n=1, 2, 3, . . . , n) are the same, and because of the connections between the transformers T1n (n=1, 2, 3, . . . , n), the power stage circuit 10 and the lamps L1n (n=1, 2, 3, . . . , n) are also the same, each transformer T1n (n=1, 2, 3, . . . , n) provides the same voltage in phase and the same voltage value to each of the lamps L1n (n=1, 2, 3, . . . , n). However, currents flowing through the lamps L1n (n=1, 2, 3, . . . , n) are unbalanced. The imbalanced currents deteriorate illumination uniformity of the LCD panel.
FIG. 7 shows another schematic diagram of a conventional driving device. The conventional driving device as shown in FIG. 7 is substantially the same as that of the driving device in FIG. 6, except that the first inputs a2n (n=1, 3, 5, . . . , (2n−1)) of the primary windings of the transformers T2n (n=1, 3, 5, . . . , (2n−1)) and the second inputs b2n (n=2, 4, 6, . . . , 2n) of the primary windings of the transformers T2n (n=2, 4, 6, . . . , 2n) are jointly connected to one output of the power stage circuit 20, and the second inputs b2n (n=1, 3, 5, . . . , (2n−1)) of the primary windings of the transformers T2n (n=1, 3, 5, . . . , (2n−1)) and the first inputs a2 (n=2, 4, 6, . . . , 2n) of the primary windings of the transformers T2n (n=2, 4, 6, . . . , 2n) are jointly connected to another output of the power stage circuit 20.
In the conventional driving device of FIG. 7, voltage values output from two adjacent lamps L1n (n=1, 2, 3, . . . , n) are the same magnitude, but 180 degrees out of phase. Consequently, currents flowing through the lamps L1n (n=1, 2, 3, . . . , n) are balanced such that illumination of the LCD panel is consistent. However, arcing may occur between adjacent lamps, due to high voltage differences. In order to avoid arcing, distance between the circuitries should be increased or holes formed in the circuit board.
However, increased distance between lamps, increases the size of the circuit board, and holes in the circuit board reduce physical integrity of the circuit board.